Either way we're poorly equipped to handle a worst-case scenario, should this come to pass. Nice reading material on this topic would be James Hansen, a merited professor in NASA's employ (they've been to the moon and back, wich is more than you can say about Exxon Mobil, or Royal Dutch Shell).
Funny language like
Multiple positive feedbacks accelerate the process once it is underway.
The global mean temperature three million years ago was only 2–3 °C warmer than today, while the sea level was 25 ± 10 m higher
proves interesting for sure.
The whole reason this is surprising, is that Hansen, maintains that this is a posibility that we see climate along the lines of this once again, within the immediate future(that being 5m in about 100 years time). This is an estimate that is about 10 times more dramatic than IPCC have proposed(58cm, at most), and not at all satisfying to think about.
Consider this; where are you at 5m higher sea level? And your immediate infrastructure, and your national and international economic system. It's long story short a challenge of impossibly big proportions, and a perfectly natural human reflex is to shy away from problems at this scale. And then we're not even talking of the consequences of the new and exiting weather pattern.. It just might be time to grow your own potatoes again.
Why the big difference in numbers? IPCC have to be 110% sure of any statement they put out, so naturally they're vague about effects that they do not have a good predictive model of. Possible rapid dynamical response of the ice sheet, is one of the factors that are impossible to estimate with a high level of confidence, and are therefore not included in the IPCC models. Wich is a shame.